1. Field of the Invention
The present invention relates to the field of the display of images and, in particular, to projection display devices using a video projector with several projection tubes (at least one group of three tubes for the three components, red, green and blue).
Projection display devices give images having faults of geometry, convergence, focusing, colorimetry and uniformity resulting as much from defects in the projection tubes themselves and their optic systems as from the differences in the characteristics of these tubes, leading to a poor superimposition of the colors. These faults need to be corrected in order to obtain a quality image at every point of the surface of this image.
2. Description of the Related Art
To overcome these drawbacks, instead of having recourse to delicate manual adjustments, it has been proposed to make use of a negative feedback loop. This negative feedback loop uses an image retaking device to detect and then automatically correct certain of these faults. This fault detection method is based on a sequential analysis of reference pixels equidistributed on a projected test image. A processing of this type cannot be used to analyze the variations due to instances of non-uniformity in an entire image, for example non-uniformity of brilliance or colorimetry, but can be used only to analyze variations in shape, notably variations in geometry, convergence or focusing. Moreover the variations due to the temporal drift of the localization of the pixel, for example resulting from thermal drifts affecting the characteristics of the projection tubes, cannot be corrected without adding on a complex self-correlation processing operation. This means that such a system cannot be used to make a full correction of the entire projected image. In particular, it is not possible to make a correction of uniformity of brilliance or a correction of colorimetry.